A folding machine is known to be associated with a creasing unit for performing auxiliary creasing operations, i.e. forming crease lines on sheets to assist subsequent folding. Creasing is particularly necessary when working with thick sheets or sheets plastic-coated on one or both sides.
A creasing unit with a rotating circular blade is known to be located in series with a folding unit to form creases lengthwise with respect to the travelling direction of the sheets. This solution permits continuous operation, i.e. without stopping the sheets to form the creases, but is limited in scope, by not allowing for transverse creases for use on a pocket-type folding unit, and by having a tendency to damage the paper.
A creasing unit with a reciprocating blade is also known to be located upstream from the folding unit to form creases crosswise to the travelling direction of the sheets for use at the subsequent folding stage. A reciprocating-blade unit, however, calls for stopping the sheet, and the creasing operation, though excellent from the technical standpoint and variously controllable, is relatively slow and fails to make the best use of the machine's output potential.